Low voltage-high current switch means employing an expendable arcing contact assembly



Feb. 10, 1970 s. o. RODESEIKE ET AL 3,495,055

LOW VOLTAGE-HIGH CURRENT SWITCH MEANS EMPLOYING AN EXPENDABLE ARCING CONTACT ASSEMBLY Filed April 13. 1967 I 3 Sheets-Sheet 1 .IIEJ a- L /4 2'5 /3 Q Z/Jf H. Z2 Z5 I I "I 3/ if lying INVENTORY BY FHA /v W. JAM/'4 Feb. 10, 1970 s. o. RODESEIKE ET AL 3,495,055

LOW VOLTAGE-HIGH CURRENT SWITCH MEANS EMPLOYING AN EXPENDABLE ARCING CONTACT ASSEMBLY Filed April 13, 1967 3 Sheets-Sheet 3 United States Patent U.S. Cl. 200-146 7 Claims ABSTRACT OF THE DISCLOSURE This disclosure teaches a switch preferably adapted for use in low voltage-high current circuits having a high opening and closing operating duty in which the main cooperating contacts are called upon to provide excellent contact engagement and an extremely low voltage drop across the bridging contacts. In order to insure the fact that the contact engagement and voltage drop across the bridging main contacts is extremely low, it is important to provide an arcing contact structure cooperatively related to the main contact structure so that the arcing contacts will close prior to closure of the main contacts, and further so that the arcing contacts will open subsequent to the disengagement of the main contacts. An

,arrangement of this type thereby imposes a heavy duty BACKGROUND OF THE INVENTION The arcing contact assembly is arranged so as to be operated between the engaged and disengaged positions by the same cam means which control engagement and disengagement of the main contacts. The movable arcing contact is comprised of a resilient member which is biased to move in the direction away from closure with the actual position obtained by the movable arcing contact being controlled by the location of the switch cam assembly. The actual location of the arcing stationary contact and the opposed contact surface of the arcing movable contact is such that these contacts are completely exposed to view and are free to be removed and replaced if and when needed, regardless of the fact that the switch may be in either the closed current carrying state or the open inactive state. Suitable keying means are provided on the arcing contact structures so as to permit assembly and disassembly with the need for removing only three fastening means While, at the same time, assuring proper alignment thereof.

Forked prongs are provided on the arcing contact movable assembly to act as a prying lever to facilitate contact separation in the event that the arcing contacts would tend to weld. The arcing contact assembly is of relatively low mass, and its relationship to the switch operating cam is such as to cause the arcing contacts to break or separate at much greater speeds than that at which the main contacts break. This arrangement significantly reduces the arcing display and burning when the switch opens so as to markedly increase the useful operating life of the contact assembly. The advantageous positioning of the arcing contact assembly, in addition to being fully exposed to view, provides more than adequate clearance for assembly and disassembly operations so as to permit changing of the contacting surfaces without any need whatsoever for either removal or disassembly of the switch from the circuit in which it is employed.

The instant invention relates to switches, and more particularly to a novel arcing contact assembly for use in switches of the low Voltage-high current type wherein simple assembly and disassembly of the expendable arcing contact surfaces is permitted without any need whatsoever for disassembly of the switch means and in which the breaking movement of the arcing contacts during an opening operation is greatly facilitated so as to insure a longer useful operating life of the arcing contact assembly.

There are a number of applications in which switches are provided for short circuiting energy sources so as to avoid the need for shutting down the entire power supply to inspect and repair defective cells. For example, in electrolytic process operations, voltage across cells employed in such operations is generally of the order of 3 to 6 volts and, in most cases, 10 volts or less. Cells of this type, however, normally carry very high current of the order of tens of thousands of amperes. Such cells are typically connected in series, rather than in parallel, so that if any of these cells become defective for any reason it would be necessary to shut down the entire line to make an inspection and repair the defective cell.

It is Well known in the prior art, as discussed in U.S. Patent No. 2,743,338, issued April 24, 1956 to H. W. Graybill, entitled Low Voltage, High Current Switch, assigned to the assignee of the instant invention, to insert a switch across the defective cell would act as a shunt circuit in the series system, allowing withdrawal of the cell from the system without shutting down the entire line.

Since such systems carry very large currents, switches employed as shunting devices in the system must be capable of carrying such extremely large currents with only extremely small voltage drops across the bridging con tacts.

Whereas the voltages across such cells usually of the order of 10 volts or less, the extremely large currents which pass through these shunting switches are known to cause arcing during contact engagement and disengagement. In order to reduce pitting or other damage to the bridging contacts to a minimum, it is conventional in the prior art to provide an arcing contact assembly which is designed to close just prior to the main contacts of the switch, and further designed to open just subsequent to the opening of the main contacts of the switch so that any arcing which might occur will be diverted and limited to the arcing contact assemblies, thereby substantially eliminating any pitting or other damage to the main bridging contacts.

In conventional switches, the arcing contact assemblies have been either included as an integral part of the main contact assembly or has been constructed so as to be positioned to one side of the main contact structure. Since the arcing contact assemblies experience all of the arcing during opening and closing operations to the exclusion of the main bridging contacts, the arcing contact assemblies have a much shorter useful operating life than the main contacts, thereby necessitating the replacement of the arcing contact assemblies much more frequently than replacement of the main bridging contacts of the switch assembly. Conventional structures which are designed as above described necessitate disassembly of the entire switch structure which, in turn, requires that the switch structure be removed from the circuit in which it is employed for replacement of the arcing contact assemblies, thereby making inspection, disassembly and assembly rather tedious and involved operations.

In the instant invention, there is provided a novel arcing contact assembly which is completely exposed to view so as to greatly facilitate inspection of the arcing contacts. In addition thereto, the arcing contact surfaces may be removed and replaced without any necessity whatsoever for disassembling or otherwise operating upon the main switch components during either an inspection or replacement operation. The arcing contact assembly is further formed of elements having low mass which operate with the cam means of the switch to produce greatly accelerated breaking speeds during the disengagement operation of the arcing contacts so as to markedly lengthen their useful operating lives.

The switch means of the instant invention is comprised of a plurality of movable main contacts having a substantially hemispherical contact surface for engagement with first and second engaging surfaces of main stationary contact members. The main movable contact members are pivotally linked to cam means rotatable with an operating shaft for moving the main movable contacts into and out of engagement with the main stationary contact.

The arcing contact assembly is comprised of a stationary arcing contact member secured to one of said main stationary contacts so as to be in electrical circuit therewith. The stationary arcing contact may be removed and replaced simply through the removal of two fastening means.

The movable arcing contact structure is comprised of an arcing contact spring which is comprised of a suitable conductive material stamped and formed so as to exhibit a suitable amount of resiliency. The first end of the arcing contact spring is secured to the remaining main stationary contact so as to be in electrical circuit therewith. An intermediate portion of the arcing contact spring is designed to make wiping engagement with the cam means controlling the operation of the main movable contacts. The opposite end of the arcing contact spring is provided with an opening for receiving the arcing movable contact structure coupled thereto with suitable single fastening means. The arcing movable contact is provided with a projection which cooperates with a second opening in the arcing contact spring to assure proper alignment of the arcing movable contact while requiring only single fastening means for securement. The arcing contact spring is further provided with a pair of forked prongs to facilitate prying upward of the arcing contact spring in the case where the arcing contacts may tend to weld. The actual location of the arcing movable and stationary contacts is substantially removed from the location of the main bridging contact so as to place the arcing contacts in clear view for inspection purposes, as well as to enable assembly and disassembly of the arcing contacts without any need whatsoever for disassembly of the switch structure. Low mass of the arcing contact structure provides accelerated breaking speeds as compared with conventional devices so as to markedly reduce arcing during a disengagement operation, thereby significantly increasing the useful operating life of the arcing contact assembly.

SUMMARY OF THE INVENTION It is, therefore, one object of the instant invention to provide a novel switch having main and arcing contact assemblies operative through a single cam means, wherein the arcing contact assembly is so designed as to greatly facilitate inspection, disassembly and assembly without any need whatsoever for disassembly of the switch means.

Another object of the instant invention is to provide novel switch means comprised of main and arcing contact assemblies wherein the arcing contact assembly is of much smaller mass than the main contact assemblies to enable accelerated breaking speeds during disengagement operation to greatly reduce arcing between the arcing contacts.

Still another object of the instant invention is to provide novel switch means comprised of main and arcing contact assemblies operative by a single cam means wherein the arcing movable and stationary contacts may be removed and replaced through the removal of only three fastening means.

Another object of the instant invention is to provide novel switch means comprised of a plurality of main contacts and at least one pair of arcing contacts, all operative by single cam means wherein the arcing contact assembly is provided with forked prongs to facilitate the prying open of the arcing contact assemblies if they tend to weld.

Still another object of the instant invention is to provide novel switch means comprised of a plurality of main contact pairs and at least one arcing contact assembly, all operative under the control of single cam means wherein the speed at which the arcing contacts separate is greater than that at which the main contacts separate, due to the manner in which the cam action is applied to the arcing contact spring member.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects of the instant invention will become apparent when reading the acocmpanying description and drawings in which:

FIGURE 1a is a perspective view showing the switch means designed in accordance with the principles of the instant invention.

FIGURE lb is a perspectiveview of the rear of the switch means shown in FIGURE 1a.

FIGURE 2 is an end view partially in cross-section of the switch means of FIGURES 1a and 11) showing the main and arcing contacts in the closed (engaged) position.

FIGURE 3 is an end view partially in cross-section showing the switch means of FIGURES 1a and lb with the main and arcing contacts in the disengaged position.

FIGURE 3a is atop plan view of a portion of the switch shown in FIGURE 3.

FIGURE 4 is a perspective view showing the expendable arcing contact assembly in FIGURES 1a through 3a in greater detail.

DESCRIPTION OF THE PREFERRED EMBODIMENTS which are force-fitted directly into the side plates 15 and 16, respectively. Pins 17 and 18 are secured to shaft 11 near the facing surfaces of side plates Hand 16 to prevent movement of shaft 11 along its longitudinal axis 11a relative to the side plates 15, 16. The operating shaft 11 is provided with radially aligned holes 19 and 19a for coupling to an operating handle (not shown) to permit clockwise and counterclockwise rotation of the shaft for switch operation.

A switch cam assembly 20 is comprised of an elongated plate 21 stamped from a suitable material to form a plurality of openings 22. The elongated plate 21 is bent to form a substantially U-shaped configuration, as can best be seen in the end views of FIGURES 2 and 3. This U- shaped or hairpin configuration receives an elongated rod 23 threaded through the opening formed by the U-shaped configuration. The upper ends of the U-shaped configuration are welded or otherwise secured to the surface of shaft 11. FIGURE 1a shows some of the welds 21w joining sheet 21 to shaft 11.

Each of the openings 22 stamped in U-shaped plate 21 receives a main movable contact assembly 24 which is comprised of a hairpin-shaped substantially flat metallic member 25 which is designed to be received within an associated slot or opening 22 so as to embrace rod 23. The lower ends of hairpin-shaped element 25 are bent outwardly to form a pair of feet 26 which receive suitable fastening means 27 for securing each of the hairpinshaped members 25 to a substantially hemispheric-shaped movable main contact 28.

Each of the main movable contact assemblies 24 is further comprised of a helical biasing spring 29 whose lower end bears against the feet 26 of hairpin-shaped memher 25 and whose upper end bears against an elongated plate 30 having elongated slots (not shown) to permit the passage of the arms of the hairpin-shaped element 25 therethrough. The helical spring means 29 provides the contact wiping functions during opening and closing operations, as well as insuring rigid engagement between bridging main contacts in a manner to be more fully described.

Each of the main movable contact structures 24 are adapted to engage an associated beveled or diagonal contact surface of the stationary terminals 31 and 32, the beveled surfaces being designated by the numerals 31a and 32a, respectively.

The side plates and 16 are held in spaced parallel fashion shown best in FIGURES 1a and 1b by means of a substantially U-shaped supporting plate 33 having downwardly depending arms 33a and 33b which are rigidly fastened to side plates 15 and 16, respectively, by fastening means 34 (not all of which are exposed to view in any one figure).

The terminals 31 and 32 are rigidly held in place by the U-shaped supporting plate 33 and are secured thereto by a plurality of fastening assemblies 35, only one of which is shown in detail for purposes of simplicity, it being understood that the remaining fastening assemblies are substantially identical in design and function. As shown best in FIGURE 2, the fastening assembly 35 is comprised of elongated bolt 36 whose head 36a rests upon the surface of terminal 31 (see FIG. 1b). Since the terminals 31 and 32 as well as the U-shaped supporting plate 33 are all formed of a conductive material, an insulting collar 37 is provided which surrounds the bolt 36 so as to electrically insulate it from supporting plate 33. An insulating spacer 38 is positioned between terminal 31 and supporting plate 33, and a second insulating spacer 39 is provided between the underside of supporting plate 33 and a washer member 40. A nut 41 rigidly compresses insulating spacers 38 and 39 so as to rigidly secure terminal 31 in spaced relationship to supporting plate 33. It can clearly be seen that terminal 32 is positioned and supported in a substantially identical manner through the use of fastening assemblies substantially identical to assembly 35. Additional supporting strength for the structure may be provided through the use of a reinforcing rib 33d which is a substantially elongated plate aligned perpendicular to the surface of U-shaped supporting plate 33 and secured thereto in any suitable fashion, such as, for example, by welding.

As shown best in FIGURES 1a and lb, the main bridging contact stiucture is comprised of four movable main contact assemblies, all of which cooperate with discrete regions along the diagonally aligned contact surfaces 31a and 32a of terminals 31 and 32. It can clearly be seen that the centrally located slot 22 provided in elongated U- shaped plate 21 does not receive any movable main contact assembly 24 so as to provide a locale for positioning the arcing contact structure.

The arcing contact structure is comprised of an arcing contact spring member 42 which is a stamped and formed spring in one application having a thickness of 0.125 inch and being formed from a beryllium copper strip. It should be understood, however, that the thickness and material composition may vary depending upon the particular application involved.

The left-hand end of the arcing contact spring member 42 relative to FIGURES 3 and 4 is bent under at 43 and is provided with a pair of apertures 44 (see FIG. 4) to receive fastening means 45a which rigidly secure and electrically couple left-hand end of the arcing spring member to terminal 31. The section 42a of spring member 42 adjacent the bent under-portion 43a is substantially straight and is aligned substantially diagonally relative to the surfaces of the terminals 31 and 32. The section 46 of the arcing spring member adjacent the straight portion is bent downwardly so as to form the intermediate portion 45 which is a substantially curved or arcuate-shaped configuration to facilitate wiping engagement with the switch cam means 21 in a manner to be more fully described. The outer portions 47 of the straight-line section 42a on opposing sides of the central section 45 continue upwardly along the diagonal line so as to form forked prying means to facilitate the opening operation in a manner to be more fully described.

The right-hand portion of section 45 is bent downwardly at 48 to form a downwardly depending section 49 which receives the disposable moving contact assembly 50. The disposable moving contact assembly 50 is comprised of a flat metallic plate preferably formed of copper having a bent-over projection 51 at its upper end, an opening 52 provided near its center, and having a suitable contact surface 53 of relatively high conductivity brazed along its lower edge. The expendable arcing contact assembly 50 is rigidly secured to the arcing spring member 42 by fastening member 54 which is passed through opening 52 in expendable contact assembly 50 and which threadedly engages the plug-nut 55 rigidly secured to the surface of downwardly depending section 49 which is opposite the surface upon which the expendable contact assembly 50 is secured. The bent-over projection 51 registers in opening 51a to position the movable contact assembly 50.

The expendable stationary arcing contact assembly 56 is comprised of a substantially flat plate 57 of conductive material, preferably copper, which is provided with a pair of apertures 53 for receiving fastening means 57a to secure assembly 56 to and place assembly 56 in electrical circuit with terminal 32. A suitable contact surface 59 formed of a highly conductive and good wearing material is brazed to the upper surface of conductive plate 57.

The operation of the switch means is as follows:

Let is first be assumed that the switch means 10 is in the open or disengaged position, as can best be seen in FIGURE 3. Operation to the closed position is caused by rotating shaft 11 (through suitable operating means which are not shown) counterclockwise as shown by arrow 60. Since all of the movable main contact assemblies 24 operate in a substantially similar fashion, only one of these contact assemblies will be described in setting forth the closing operation, it being understood that all of the remaining movable main contact assemblies engage their associated regions of terminals 31 and 32 in a similar fashion. Also, as is obvious from the prior art, each will be seated independently of one another so as to assure firm engagement between mating contact surfaces with the bridging resistance therebetween being extremely small.

The rotation of shaft 11 in the counterclockwise direction, as shown by arrow 60, causes each substantially hemispheric contact surface 28 to move substantially diagonally along the line 61 in the direction shown by the arrowhead carried on this line. The movable contact element 28 is guided toward the diagonal contact surfaces 31a and 32a by means of the contact guides 62 and 63 which are substantially L-shaped elongated insulating members secured to the surfaces of terminals 31 and 32 by suitable fastening means. In one preferred embodiment, the contact guides 62 and 63 are formed of Fiberglas of a suitable thickness and strength, but any other material may be provided if desired, depending only upon the needs of the user.

Each of the movable main contacts 28 continue to move downwardly until they make engagement with the diagonally aligned contact surfaces 31a and 32a. At this time, due to the rotation of the cam means 21, the contacts experience rotational movement, causing their longitudinal axes to move from the diagonal alignment, as shown by line 61, toward the vertical alignment, as shown by line 64, causing a wiping action to occur between the mating surfaces of contacts 28 and the terminals 31 and 32. This high pressure wiping action removes any dirt or corrosion from the contact surfaces, and the helical spring member 29 which is compressed during the rotational movement insures the high pressure wiping action, as well as providing rigid contact engagement between the mating surfaces.

It is important to note that during the time the cam member 21 is moving the contact members 28 in a direction substantially along the diagonal line 61, the outer surface of the cam member 21 bears against and makes wiping contact with the upper surface of the arcuate section 45 or arcing spring 42. The relationship as between arcuate section 45 and cam 21 is such that the resilient arcing contact spring 42, which is normally biased so as to be urged vertically upward, as shown by arrow 65 in FIGURE 2, is urged in the downward vertical direction, causing the contact surface 53 to be urged into engagement with the contact surface 59 prior to the time at which the main bridging contacts are engaged, so that any arcing which may occur during contact closure is diverted to the arcing contacts 53, 59.

The final position (i.e., the fully closed position) of the switch means is shown in FIGURE 2 wherein both the main and arcing contact assemblies are rigidly held in the engaged position. Again, it should be noted that the arcing contacts 53-59 close before the main contacts 28 31, 32 to assure the fact that any arcing which occurs during closing operation will be restricted to the arcing contacts 53, 59.

To perform an opening operation, shaft 11 is rotated clockwise, as shown by arrow 67. During the initial movement of cam means 21, hemispherical-shaped contact members 28 are rotated or rocked relative to terminals 31 and 32 so as to again perform a high pressure wiping action, due to the helical spring 29 which is highly compressed at this time, thereby again performing a selfwiping or self-cleaning function for the mating surfaces of the main contact structure. The timing relationship between the main and arcing contact structures is such that the cam 21 will allow the arcing spring member 42 to be lifted as a result of its resiliency in the upward direction, as shown by arrow 65, causing the arcing contacts 53, 59 to separate after to the separation of main contacts 28 from their engaging surfaces 31a and 32a of terminals 31 and 32, respectively. The speed at which the arcing contacts break or separate is greater than that at which the main contacts break. This is accomplished by the manner in which the cam action is applied to the arcing spring member 42. The increase in breaking speed reduces the arcing display and the burning or pitting of contacts 53, 59 as the switch opens. Since the arcing contact structures are of much lower mass than the main contact structures, breaking speed of the arcing contact structures during the opening operation is still further facilitated.

The arcing contact assembly of the instant invention can be installed in standard switches of this type already found in field use, and requires no additional clearances for applications of such standard switches. The positioning of the contact assemblies 50 and 56 relative to the main contact assemblies 24 and 31a32a is such as to place the contact surfaces 53, 59 in full view for inspection purposes. In addition thereto, these expendable assemblies 50 and 56 are easily replaced through the use of a screw-driver S, as shown in FIGURE 3, wherein both expandable assemblies 50 and 56 may be completely removed and replaced through the removal of only three screws. Also, the expendable portions of the arcing contact can be replaced while the switch is open and still connected in circuit. The only protection that need be considered is that of employing a screw-driver with an insulated shank and handle.

The forked prongs 47, 47 provided along arcing spring member 32 facilitate the separation of the arcing contacts 53, 59 in the case where these contacts tend to weld. The prying operation is performed by rotating shaft 11 Q QGliWiSQ in the direction shown by arrow 67 of FIGURE 2, causing the cam means to bear against the underside of prongs 47, 47 in order to separate arcing contacts 53, 59.

It can, therefore, be seen that the instant invention provides a novel switch means comprised of a plurality of main contact assemblies and at least one arcing contact assembly wherein the arcing contact assembly is designed to have its expendable contacts in full view to greatly facilitate inspection thereof and to permit removal and replacement of the expendable contacts without any need whatsoever for disassembling the entire switch assembly. One of the expendable contacts, namely, the movable arcing contact is secured to an arcing spring element which is of relatively low mass compared to the main movable contact assemblies so as to permit relatively high speed separation during an opening operation in order to minimize arcing display and burning or pitting of the contact surfaces 53, 59 forming the arcing contact assembly. Exhaustive experimentation conducted on switches of the type described herein carrying over 5,000 amperers at a voltage of less than 5 volts indicated that the switches are capable of carrying full load without overheating after the performance of 1,000 opening and closing operations. The resistance of the switches tested after 1,000 operations showed that they were not only still functional, but that they have worn-in with the resistances after the test being substantially lower than the resistances before the test, both of these resistances being less than 2% micro-ohms. The arcing contacts were found to be still good for future operations.

In the foregoing, we have described our invention only in connection with referred specific embodiments and applications thereof. Many variations and modifications of the principles of our invention within the scope of the description herein are obvious. For example, whereas the arcing contact assembly is shown as being positioned at the center of the switch structure, it is obvious that the arcing contact structure could be positioned at one end thereof, or more than one arcing contact structure may be employed, both being positioned toward the center, or at opposite ends thereof, or in any other suitable arrangement What is claimed is:

1. In a switch having a plurality of movable contacts and a pair of stationary contacts having opposing surfaces forming a wedge shaped gap therebetween;

control means for simultaneously moving said movable contacts into said gap region for engagement with said stationary contacts;

the improvement comprising:

first arcing contact means secured to and in electrical circuit with one of said stationary contacts and being spaced distance from one side of said gap;

second arcing contact means for cooperative engagement with said first arcing contact means;

arcing spring means having a first end secured to and in electrical circuit with the remaining stationary contact and being positioned on the opposite side of said gap;

said arcing spring means extending over said gap toward said first arcing contact means and having its free end adapted for releasably securing said second arcing contact means thereto;

said arcing spring means normally biasing said first and second arcing contact means toward disengagement;

said control means slidingly engaging the intermediate portion of said arcing spring means to urge said first and second arcing contact means into engagement prior to engagement of said movable contacts with said stationary contacts.

2. The switch of claim 1 wherein said first arcing contact means is comprised of a contact surface of a highconductivity-hard wearing conductive material secured to a flat conductive plate;

removable threaded fastening means for securing said first arcing contact means to said one stationary contact to facilitate removal and replacement activities.

3. The switch of c aim 1 wherein said second arcing contact means is comprised of a contact surface of a high-conductivity-hard wearing conductive material secured to a flat conductive plate;

removable threaded fastening means for securing said second arcing contact means to said arcing spring means.

4. The switch of claim 3 wherein said fiat conductive plate is provided with a projection and said arcing spring means is provided with a cooperating aperture for properly aligning said second arcing contact means.

5. The switch of claim 1 wherein said control means is comprised of a rotatably mounted shaft; elongated ca-m means extending outwardly from one portion of said shaft and being substantially parallel to the axis of said shaft for engaging all of said movable contacts and the 20 intermediate portion of said arcing spring means to cause engagement of said first and second arcing contact means prior to the engagement of said movable and stationary contacts when said shaft is rotated in a first direction and to cause disengagement of said first and second arcing contact means subsequent to disengagement of said movable and stationary contacts when said shaft is rotated in a second direction opposite said first direction.

6. The switch of claim 5 wherein the arcing spring means intermediate portion engaging said cam means is curved to control the opening and closing relationship of said arcing contacts and said movable and stationary contacts.

7. The switch of claim 5 wherein said arcing spring means is further comprised of prongs lying adjacent said cam means and engageable therewith when said shaft is rotated in said second direction to pry open said arcing contacts as a result of contacts welding.

References Cited UNITED STATES PATENTS 1,244,225 10/ 1917' Mayer 200-146 1,683,280 9/1928 Arthur 200-146X FOREIGN PATENTS 77,084 1948 Czechoslovakia.

ROBERT S. MACON, Primary Examiner 

